In-service airplanes undergo regular inspections of various locations on the fuselage to detect various defects, such as cracks or imperfections. These inspections affect thousands of aircraft, with each aircraft undergoing inspection of tens of thousands of fastener locations. For instance, these locations can include fastener locations, doubler edges, and the like.
Eddy current inspections of fastener locations containing flush head fasteners account for a large percentage of the eddy current inspections performed on in-service airplanes. The current approach to eddy current inspections involves using a circle template to align an eddy current probe so that the probe can be translated around the perimeter of the fastener. Alignment of the probe with respect to the fastener is critical. If the probe passes over the interface between the fastener and the skin of the aircraft surface, a false crack signal will occur and the template must be repositioned to ensure that there is actually a crack and not just the false signal. This process is tedious, slow, and prone to mistakes. In addition, eddy current inspections are among the most time consuming inspection methods to perform and are not desirable for large inspection areas.
Current eddy probe inspections also involve various disadvantages. One disadvantage is that if the paint on the airplane is too thick, it must be stripped to permit alignment of the standard eddy current pencil or spot probes. Stripping the paint in this manner is costly and invasive since the paint will then need to be repaired after inspection. Another disadvantage is that eddy probe inspections are typically time intensive. For a typical fuselage, there can be more than 10,000 fasteners. Because the primary inspection method requires a ⅛ inch diameter probe to be manually raster scanned over the full perimeter of all the doubler edges on the fuselage of these airplanes, inspection of a single aircraft can take a significant amount of time. Yet another disadvantage is that typical inspection methods are limited to detecting surface cracks.
An alternative to manual probe inspections requires purchasing an entirely new system with a unique probe. In particular, a custom designed probe device can be produced for each size of fastener and probe. However, because there is a range of fastener sizes, numerous probe devices with special instruments would need to be produced, stored, and maintained in order to implement this alternative. Accordingly, these custom designed systems are costly, and not commonly used in the inspection of aircraft.
Current inspection methods continue to be tedious, time consuming, and prone to errors. In addition, conventional inspection apparatuses are typically limited to detecting surface cracks and may in some cases require the removal of paint from the airplane surface, thereby adding to costs and downtime. Consequently, there is a need for low cost, low skill inspection solutions that can be used to increase inspection reliability and also decrease inspector fatigue and inspection time.